The present invention relates to a new technology for producing a spread sheet made of a multi-filament (also including a tow spread sheet) comprising plural filaments combined together, more specifically, it relates to an epoch-making method of efficiently mass-producing a high-quality multi-filament spread sheet whose filaments are spread in such a manner that they are orderly disposed in parallel to each other without the quality deterioration by using a ready-made multi-filament as a production material, for instance, such a multi-filament spread sheet as being excellent in impregnation with resin and filament alignment which are indispensable for a supplemental fiber material for reinforcing a matrix so as to produce a complex material and the apparatus used in the same as well as the multi-filament spread sheet produced in the same.
In recent years, there have been developed and sold on the market a number of complex materials where a carbon fiber, a glass fiber or aromatic polyamide filament such as KEVLAR 49 are mixed with a matrix such as a synthetic resin and the like or interposed between the layers of the matrix for reinforcement.
Because those complex materials show excellent performance in such aspects as durability, heating and corrosion resistance, electrical characteristics and weight reduction, such various industries as aerospace, inland transportation, shipping, construction, civil engineering, industrial parts production, sports goods are selectively using such complex materials as mentioned above in accordance with their type of production so that those complex materials are in acute demand on the market.
In this connection, there are such practical forms of use of those fibers for reinforcing a matrix as plural filaments either disposed in a required width or cut off in a fixed size or processed in cloth status like woven, knitted, braided fabric or nonwoven fabric. Those fibers are either directly complexed with a matrix or processed into a work-in-process called preimpregnation by impregnating a sheet or a woven fabric and so forth on which plural filaments are regularly disposed with a synthetic resin. After the required number of said works-in-process is piled up one over another, they are processed into a finished product by means of a device such as an autoclave.
By the way, the most conspicuous complex materials in recent years above all are such high-function fiber materials as the aforesaid carbon fiber, aromatic polyamide filament and ceramic fiber which are used for reinforcing a matrix such as a synthetic resin. Those high-function fiber materials are normally supplied in multi-filament status where plural filaments are bundled and adhered together with a sizing agent. In the event where such multi-filaments as mentioned above are put to use as supplemental fiber materials for reinforcing a matrix, it is necessary to structurally strengthen adhesion between each filament and said matrix by enlarging the contact area therebetween. In order to satisfy this requirement, it is effective to thinly spread those multi-filaments in sheetlike shape. In other words, a complex material can not play its effective and important role without being structured in such a manner that the surface of each filament attaches to and firmly clings to a matrix.
However, in fact, it is extremely difficult to uniformly impregnate the interval between adjoining filaments with a matrix especially in the event where a multi-filament is used as a supplemental fiber material for reinforcing said matrix. Thus, in order to solve the aforesaid issue, said multi-filament is thinly spread in sheetlike shape within a fixed width so that the interstices among the filaments are impregnated with a matrix such as a synthetic resin.
In this connection, a conventional way of flatly spreading a multi-filament is performed during the process where said multi-filament is released from a yarn supply section and goes on to be wound on a yarn winding cylinder. The following methods for that purpose are well-known among the concerned.
1 A static method where static electricity is acted on a multi-filament on the move while a certain tension is imparted thereto in order to cause counteraction among individual filaments so as to spread the multi-filament. PA1 2 A pressing method where a multi-filament is pressed by revolving rollers so that it is flatly squeezed and smashed in spread shape. PA1 3 A jetting method where a multi-filament is subjected to water or air jet so that it is flatly spread. PA1 4 A ultrasound method where the sizing of adjoining filaments (e.g. by means of a sizing agent) is undone by giving ultrasound vibration to the multi-filament so as to flatly spread it.
It is the ideal state of a supplemental fiber material for reinforcing a matrix which is made of a multi-filament spread sheet that the filaments each continuously extend in straight manner without any yarn cut thereon so that they do not intermingle with one another and align in parallel to each other with maintaining a certain interval between adjoining filaments so as to be orderly disposed within a certain width.
However, any one of the aforesaid conventional methods is intended to set apart the filaments from one another so as to flatly spread them by acting such strong physical external forces as electrical counteraction, roller pressure, fluid impact and ultrasound vibration etc. on the multi-filament. Thus, in the event where the efficiency of the multi-filament spread operation is tried to improve, it is necessary to spurt strong air jet on the bundle of filaments by enhancing the air velocity especially in the case of adopting the prior jetting method.
In the event where the aforesaid external forces such as static electricity, rolling pressure, jet force and ultrasound vibration and so forth are intensified in order to enhance the efficiency of the multi-filament spread operation, a multi-filament spread sheet having such width and thinness as required can not be obtained while it unavoidably occurs that the filaments are subject to damage such as yarn cut and fluffing due to strong external forces acting on said filaments. As to such fibers vulnerable to break as carbon filament and ceramic fiber, they are damaged to the extent that they can not be put into a practical use any more.
In addition, with the aforesaid conventional ways of the multi-filament spread operation, the filaments are enforced to be separated from one another by said external forces, therefore, the filaments result in being complexly intermingled with one another so that such width and parallelism among filaments as required are difficult to obtain. Moreover, the static method as mentioned above can not be applied to such conductive fibers as carbon and metallic filaments.
Furthermore, it is normal that an untwisted multi-filament is used for the multi-filament spread operation in order to enhance its operational efficiency. Even though the multi-filament is seemingly in untwisted state seen from the whole bundle of filaments, there are some cases where the filaments are intermingled with one another partly within the bundle. The aforesaid conventional ways could not deal with those intermingled portions within the bundle of filaments. Some comments are given as follows to further explain this prior issue.
To explain in reference to FIG. 1, provided that a high-quality untwisted multi-filament which does not have such intermingled portions as mentioned above is put to use, when the multi-filament wound around a yarn supply section (1') at an angle (.tau.) is released from a releasing point (o) on said section (1'), said multi-filament will return to the shortest distance line (l) connecting a releasing fulcrum (p) on said yarn supply section and a grip point (q) on a feeding roller so that such force (.DELTA.) as indicated with an arrow in the drawing works on the multi-filament. At this time, owing to the friction of the surface of the yarn supply section against an untwisted multi-filament (F.sub.1), said multi-filament (F.sub.1) revolves so that there partly occurs twist in the multi-filament. In other words, even though there should be no twist on the multi-filament (F.sub.1) itself to be used, there posteriorly occur false twists in a part of said multi-filament when it is released from the yarn supply section so that parallelism among the spread filaments is interrupted. In this connection, the multi-filament (F.sub.1) on the yarn supply section (1') has its winding direction alternatively changed in the opposite direction every winding layer so that the revolving direction of the multi-filament (F.sub.1) alternatively changes too with the result that such false twists as an S twist and a Z twist alternatively occur on the multi-filament (F.sub.1). There are some cases where such false twists as mentioned above occur at the production stage by a multi-filament spinning manufacturer, that is to say, even though the multi-filament is in untwisted state before the yarn winding operation, false twists occur on the multi-filament at this operation.
Furthermore, with the aforesaid conventional methods of the multi-filament spread operation, it is impossible to mix different types of multi-filaments with one another or to make either different or similar types of multi-filaments a pileup sheet by piling them up one over another synchronously with the spread operation or make either different or similar types of multi-filaments a wide spread sheet by spreading them in parallel to each other.